My dynamic IP address starts with 24.x.x.x - installed your plugin (version 4.0, WP 3.4.2), went to activate it and received this error:
Plugin could not be activated because it triggered a fatal error. Reason code: sbl.spanhaus:153,2,24 ip: 24.x.x.x
I x'ed out my current IP address for obvious reasons. So I went to the spamhaus website, discovered that the entire 220.127.116.11/12 block of IP addresses is listed in their PBL database. I'm unable to remove my address from that list, site would not allow it.
So I took a look at your code, and found this in stop-spammer-registrations.php...
$iplist = array( 'sbl.spamhaus' => '.sbl.spamhaus.org', 'xbl.spamhaus' => '.xbl.spamhaus.org', 'dsbl' => '.list.dsbl.org', 'sorbs' => '.dnsbl.sorbs.net', 'spamcop' => '.bl.spamcop.net', 'ordb' => '.relays.ordb.org', 'njabl' => '.dnsbl.njabl.org'
and I commented out each spam database site one by one. Every single spam site listed in your plugins array considers 18.104.22.168/12 as a spam source. That is a significant number of comcast internet users. I would have to comment out that entire array list to be able to activate this plugin, and in doing so would defeat the purpose of said plugin.